Into the deep – Tracking Beaked Whales!

Beaked whales are deep diving predators that have evolved to forage at depths of more than 1000 meters. Very little is known about this group of mammals but they are believed to be primarily income breeders and seem to feed at every opportunity, mainly on squid. This study focuses on Cuvier's beaked whales ( Ziphius cavirostris ) in the U.S. Navy's Southern California Anti-Submarine Warfare Range (SOAR), where there are already nearly 200-bottom mounted hydrophones. An echosounder system was also introduced to measure squid density. Beaked whales can dive for up to 30 minutes at a time and the researchers have predicted that the whales encounter up to 30 prey items each dive. The study site was divided into three main areas – two areas that are already known as beaked whales foraging grounds (Eastern and Western) and one off-range area that the whales also use. This area is deeper than the other two.

Cuvier’s beaked whales clicks

Once all was in place, they listened to the clicks that the animals made when feeding. After several surveys, researchers found that at the off-range area, beaked whales have to dive 96 times to fulfil their energetic need. At the other end they only have to dive 22 times in the Western site and 6 in the Eastern, making the Eastern site the most prey abundant and therefore the best choice.

Mother and calf, drone footage in Mexico.

But because the Eastern and Western site are known for human disturbance it is becoming more likely that beaked whales are getting forced to use the off-range area more and more. Therefore, this study has opened up the discussion for the need for a marine protected area with no sonar disturbance. Many other studies show that sonar disturbance can drive the whales into beach stranding. The study also highlighted how little we know about deep sea cetaceans and their feeding preferences. The deep sea is still mostly ununderstood and unexplored and we may not ever understand how rapidly we are losing the habitats and animals that live within. And we may never know.

Reference:

Southall, B. L., Benoit-Bird, K. J., Moline, M. A., & Moretti, D. (2019). Quantifying deep-sea predator–prey dynamics: Implications of biological heterogeneity for beaked whale conservation. Journal of Applied Ecology , 56 (5), 1040–1049. https://doi.org/10.1111/1365-2664.13334